Abstract
To improve the autonomy of the biomimetic sphere robot (BSR), an underwater trajectory tracking problem was studied. Considering the thrusters saturation of the BSR, an improved model predictive control (MPC) algorithm that features processing multiple constraints was designed. With the proposed algorithm, the kinematic and dynamic models of the BSR are combined in order to establish the predictive model, and a new state-space model is designed that is based on an increment of the control input. Furthermore, to avoid the infeasibility of the cost function in the MPC controller design, a new term with a slack variable is added to the objective function, which enables the constraints to be imposed as soft constraints. The simulation results illustrate that the BSR was able to track the desired trajectory accurately and stably while using the improved MPC algorithm. Furthermore, a comparison with the traditional MPC shows that the designed MPC-based increment of the control input is small. In addition, a comparative simulation using the backstepping method verifies the effectiveness of the proposed method. Unlike previous studies that only focused on the simulation validations, in this study a series of experiments were carried out that further demonstrate the effectiveness of the improved MPC for underwater trajectory tracking of the BSR. The experimental results illustrate that the improved MPC is able to drive the BSR to quickly track the reference trajectory. When compared with a traditional MPC and the backstepping method used in the experiment, the proposed MPC-based trajectory is closer to the reference trajectory.
Highlights
With the rapid development of scientific ocean exploration, underwater robots have become one of the most important tools for exploiting and utilizing marine resources [1,2]
This paper focuses on the achievement of trajectory tracking with thrust constraints for the biomimetic spherical robot in an underwater plane
The yaw angle is measured while using a high-precision inertial measurement unit (IMU) mounted on the robot
Summary
With the rapid development of scientific ocean exploration, underwater robots have become one of the most important tools for exploiting and utilizing marine resources [1,2]. When compared with autonomous underwater vehicles (AUVs), the core feature of bionic small-scale robots refers to the capability of operating missions such as tracking ocean creatures and monitoring the marine environment in narrow underwater spaces. These small-scale biomimetic robots have been receiving increasing interest from academia. The closed-loop motion control (such as trajectory tracking, etc.) has seldom been considered, which is of primary importance for most applications. Over the past few years, a large number of studies have been dedicated to the underwater
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